Method and device for driving a turbocharger

ABSTRACT

In a method for driving a turbocharger with the aid of induction air which is fed to the turbine inlet, the compressed air which exits at the compressor outlet is guided into a turbine auxiliary inlet of the turbine, which turbine auxiliary inlet opens downstream of the turbine inlet into the turbine chamber at a point, at which the pressure in the driven state of the turbine is lower than the pressure of the air which is compressed by the turbocompressor.

This invention relates to a method of driving a turbocharger comprisinga turbine and a turbo compressor, with a housing which includes aturbine chamber having a turbine inlet and a turbine outlet, and acompressor chamber having a compressor inlet and a compressor outlet,and with a rotor having a turbine wheel arranged in the turbine chamberand a compressor wheel arranged in the compressor chamber, the methodincluding the step of driving the rotor by means of charge air suppliedto the turbine inlet. The present invention relates furthermore to adevice for implementing the method.

To develop and manufacture turbochargers, specific measurement and testpurposes including, for example, high-speed balancing operations, makeit necessary for the rotor of the turbocharger to be brought to itsmaximum operating speed or a similarly high speed. For this to beaccomplished, it is known from DE 10 2009 013 432 A1 to apply charge airto the turbine of the turbocharger, supplying in this manner thenecessary propulsive power to the rotor. The charge air conventionallyused is compressed air which may be drawn, for example, from a networkof compressed air. The amount of compressed air needed for driving isconsiderable, the more so since compressed air is, as a rule, cold, thatis, at room temperature, and the enthalpy difference in the turbine iscorrespondingly small. Compressed air as carrier of energy iscomparatively expensive, and the energy efficiency of the drive of theturbine using compressed air is unfavorable. Therefore, accelerating aturbocharger rotor to maximum operating speed by means of charge airincurs considerable expense.

In a method of the type referred to and described in DE 10 2011 054 236A1, the compressed air exiting at the compressor outlet is fed to theturbine inlet and admixed, by means of a jet pump, to the charge air fordriving the turbine wheel, which is fed in the form of a jet to theturbine inlet at a pressure higher than the air arriving from thecompressor and at a higher flow rate. In this way, added use is made ofthe compressed air supplied from the compressor side of the turbochargerfor driving the turbocharger, and the amount of charge air needed iscorrespondingly lower. Admixing by means of a jet pump requires thepressure of the air arriving from the compressor to be below thepressure of the charge air only by an amount enabling the jet pump toensure admixing by mixing the jet. The fulfillment of this conditiondepends on the respective configurations of turbine and compressor ofthe turbocharger and is not always guaranteed. Accordingly, this methodis limited to applications in which the pressure differential betweenthe pressure of the charge air and the pressure at the outlet of thecompressor is not very high.

RU 2 023 248 C1 discloses a method of testing a supercharge turbocompressor in which high-pressure air generated by a starter compressoris fed to a swiveling nozzle arranged in the first stage of a two-stageejector disposed downstream from the turbine, the first stage beingprovided with a diffuser. To perform a variety of tests, the nozzle iscapable of swiveling into the direction of travel of the medium forgenerating a pressure below atmospheric in the gas discharge end of theturbine, or into the opposite direction for generating a pressure aboveatmospheric in the gas discharge end of the turbine.

Moreover, GB 611 528 A discloses a test arrangement in which a turbineto be tested is driven by compressed air and coupled to a compressor,providing the possibility for the compressed air at the compressoroutlet to be used for driving the turbine by heating it and feeding itto the turbine inlet for augmenting the air supply.

RU 2 348 910 C1 discloses a method of testing turbochargers in which gasis injected to an inlet of the turbine and to an inlet of thecompressor, causing the compressor to be set in rotation by the turbine.No provision is made for returning the compressed air to the inlet ofthe turbine.

It is an object of the present invention to provide an improved methodof the type initially referred to, which reduces the demand for chargeair for driving the rotor of the turbocharger.

According to the present invention, this object is accomplished by themethod recited in claim 1. An advantageous device for implementing themethod is recited in claim 2.

In the method of the present invention, the compressed air exiting atthe compressor outlet is directed to a turbine auxiliary inlet whichopens downstream from the turbine inlet into the turbine chamber at asite where the pressure in driven condition of the turbine is lower thanthe pressure of the air compressed by the compressor.

With the method of the present invention, added use is made of thecompressed air supplied by the compressor of the turbocharger fordriving the rotor by feeding it to the turbine auxiliary inlet. It willbe understood, of course, that the air supplied by the compressor cannotbe sufficient for driving the rotor because losses occur in both theturbine and the compressor which have to be compensated for by anexternal energy supply in the form of charge air. In addition, a surplusof energy is needed to accomplish a short-time acceleration of the rotorto a high rotational speed. In contrast to a drive using exclusivelycharge air, the method of the invention requires a considerable smalleramount of charge air for driving the rotor, since the energy stored inthe air arriving from the compressor can be reclaimed for driving theturbine. In principle, the charge air supplied is only required to coverthe energy losses in the turbine and the compressor and the losses inthe rotor bearings. It is hence possible to reduce the consumption ofcharge air considerably by the method of the invention which affordsrelative ease of implementation. This then also results in acorresponding cost reduction for the drive of the turbocharger.

The method of the invention affords the further advantage of beinglargely independent of the turbocharger configuration and the pressureof the charge air. The pressure of the charge air in the turbine inletis reduced in the turbine chamber to about atmospheric pressure in theturbine outlet. By suitable selection of the site of the auxiliary inletbetween turbine inlet and turbine outlet, the pressure at the mouth ofthe auxiliary inlet can be therefore adjusted such as to be below thesupply pressure of the turbo compressor by an amount sufficient toachieve a pressure differential for the air arriving from the turbocompressor which is beneficial for driving the turbine.

To implement the method of the invention, a device for driving aturbocharger comprising a turbine and a turbo compressor is suitable,with a housing which includes a turbine chamber having a turbine inletand a turbine outlet, and a compressor chamber having a compressor inletand a compressor outlet, with a rotor having a turbine wheel arranged inthe turbine chamber and a compressor wheel arranged in the compressorchamber, and with a source of charge air adapted to be coupled to theturbine inlet, with the turbine chamber having a turbine auxiliary inletwhich opens downstream from the turbine inlet into the turbine chamberat a site where the pressure in driven condition of the turbine is lowerthan the pressure of the air compressed by the compressor, and whereinthe compressor outlet is adapted to be coupled to the turbine auxiliaryinlet by a line in order to direct the compressed air exiting at thecompressor outlet into the turbine auxiliary inlet.

The device of the present invention affords ease and economy ofmanufacture and convenience in handling. For increased efficiency, addedprovision may be made for guide vanes in the turbine inlet and/or in theturbine auxiliary inlet.

The method of the invention is suitable for utilization in connectionwith complete turbochargers and also turbocharger core assemblies. Inturbocharger core assemblies the housing is composed of a center casingaccommodating the rotor bearings and constituting a component part ofthe turbocharger, and of a turbine casing and a compressor casing whichare attached to the center casing, forming, respectively, the turbinechamber and the compressor chamber with associated inlets and outlets.The method of the invention is not considered limited to an applicationto turbochargers but may also find a useful application in similarlyconstructed assemblies, for example, gas generator assemblies of smallgas turbines, in order to drive these for balancing purposes or otherrequirements.

The present invention will be explained in more detail in the followingwith reference to an embodiment illustrated in the accompanying drawing.The drawing shows schematically a turbocharger with a connected chargeair drive constructed in accordance with the invention.

Represented in the drawing is a turbocharger 1 comprising a turbine 2and a turbo compressor 3. The turbocharger 1 includes a housing 4defining a turbine chamber 5 and a compressor chamber 6 and a bearingcasing 7 arranged therebetween. The housing 4 accommodates a rotor 8having a shaft 9 carried in the bearing casing 7. Mounted on the shaft 9in the turbine chamber 5 are a turbine wheel 10 and in the compressorchamber 6 a compressor wheel 11. On the motive fluid inlet side, theturbine chamber 5 is provided with an annular turbine inlet 12 whichsurrounds the turbine wheel 10 and opens radially into the turbinechamber 5, with the possibility for guide vanes 13 being arranged in itsmouth. At the front end of the turbine wheel 10, the turbine chamber 5opens into a coaxial turbine outlet 14. Between the turbine inlet 12 andthe turbine outlet 14, the turbine chamber 5 includes an annular turbineauxiliary inlet 15 which opens into the turbine chamber 5 and may haveon its mouth a nozzle ring 15 with guide vanes. The compressor chamber 6has at its front end a central compressor inlet 17 and an annularcompressor outlet 18.

To drive the turbocharger 1, for example, for measurement purposes, thecompressor outlet 18 is connected to the turbine auxiliary inlet 15 bymeans of a line 20. In addition, a line 21 connects the turbine inlet 12to a charge-air reservoir 22 to which charge air is delivered by amotor-powered compressor 23. Arranged in the line 21 is a valve 24 forcontrolling the supply of charge air. The pressure of the charge air isconsiderably higher than the maximum pressure which the compressed airsupplied from the turbo compressor 3 reaches in the compressor outlet 15at maximum operating speed.

When it is desired to drive the rotor 8 and accelerate it to a speedcorresponding preferably to the maximum operating speed, the valve 24opens, directing charge air into the turbine inlet 12. The charge airentering from there into the turbine chamber 5 drives the turbine wheel10, setting the rotor 8 in rotation. With the speed of the rotor 8increasing, the output of the turbo compressor 3 increases, too, andwith it the pressure of the compressed air in the volumetric flow fed tothe turbine auxiliary inlet 15. A pressure differential develops on theturbine auxiliary inlet 15 between the pressure of the compressed airand the pressure in the turbine chamber 5 which at this point hasalready dropped to a low pressure. The pressure differential becomesgreater with the speed, generating an air stream of high flow velocitywhich drives the turbine wheel 10. The turbine speed continues toincrease until it reaches a value at which an equilibrium is present atwhich the energy supplied with the charge air from the charge-airreservoir 22 corresponds to the energy losses in the turbine 2, in theturbo compressor 3 and in the rotor bearings. When it is desired toincrease the rotor speed still further, it is necessary to increase thesupply of charge air by suitable control of the valve 24. Conversely,the rotor speed may be lowered by reducing the supply of charge air.

Overall, by introducing the compressed air supplied by the turbocompressor 3 into the turbine 2, the necessary amount of charge air andhence the expenditure of energy and cost for a measurement and testoperation of the turbocharger 1 are significantly reduced.

1. A method of driving a turbocharger (1) comprising a turbine (2) and aturbo compressor (3), with a housing (4) which includes a turbinechamber (5) having a turbine inlet (12) and a turbine outlet (14), and acompressor chamber (6) having a compressor inlet (17) and a compressoroutlet (18), and with a rotor (8) having a turbine wheel (10) arrangedin the turbine chamber (5) and a compressor wheel (11) arranged in thecompressor chamber (6), the method including the step of driving therotor (8) by means of charge air supplied to the turbine inlet (12),wherein the compressed air exiting at the compressor outlet (18) isdirected to a turbine auxiliary inlet (15) which opens downstream fromthe turbine inlet (12) into the turbine chamber (5) at a site where thepressure in a driven condition of the turbine (2) is lower than thepressure of the air compressed by the turbo compressor (3).
 2. A devicefor driving a turbocharger (1) comprising a turbine (2) and a turbocompressor (3), with a housing (4) which includes a turbine chamber (5)having a turbine inlet (12) and a turbine outlet (14), and a compressorchamber (6) having a compressor inlet (17) and a compressor outlet (18),with a rotor (8) having a turbine wheel (10) arranged in the turbinechamber (5) and a compressor wheel (11) arranged in the compressorchamber (6), and with a source of charge air adapted to be coupled tothe turbine inlet (12), comprising a turbine auxiliary inlet (15) whichopens downstream from the turbine inlet (12) into the turbine chamber(5) at a site where the pressure in a driven condition of the turbine(2) is lower than the pressure of the air compressed by the turbocompressor (3), and by a line (20) adapted to couple the compressoroutlet (18) to the turbine auxiliary inlet (15) in order to direct thecompressed air exiting at the compressor outlet (18) into the turbineauxiliary inlet (15).
 3. The device according to claim 2, wherein guidevanes (13) are arranged in the turbine inlet and/or in the turbineauxiliary inlet.
 4. The device according to claim 2, wherein the supplyof charge air is controllable by a valve (24).